1. Field of the Invention
This invention relates to the monitoring of platen die cutting. Such structures of this type, generally, periodically examine the force profiles from a strain gage mounted near the platen die cutter mouth. This system measures not only the maximum forces developed, but also monitors other features of the loading curve, such as the paper-bursting point. Quality of cutting, as well as die wear, can be more readily assessed with this additional information and adjustments made to improve cutting results before the adverse effects show in visual inspections of the product.
2. Description of the Related Art
In platen die cutting of paperboard, die wear and maladjustment show as incomplete or partial cuts in the final product. The usual method of determining the state of the die is to visually inspect samples of the cut paper. If partial cuts are observed, the platen die must be adjusted or replaced. A typical adjustment is to increase the pressure or tonnage on the die, and thus increase the cutting force.
It is known to examine the maximum cutting force or have as a goal to keep a constant force using some actuator. Exemplary of such prior art is U.S. Pat. No. 4,812,984 (""984) to M. Yerly et al., entitledxe2x80x9cMethod and Device for Measuring the Cutting Forces and Limiting Overloads of the Cutting Force in a Platen Pressxe2x80x9d. While the ""984 reference employs a device to measure the forces statically, the further advantageous system would be one which measured the forces dynamically.
It is also known to employ a device which determines tool wear or prevents overload of the machinery. Exemplary of such prior art is U.S. Pat. No. 5,599,142 (""142) to A. Fujimoto et al., entitled xe2x80x9cDrilling Control Apparatus.xe2x80x9d While the ""142 reference determines tool wear or prevents machinery overload, its emphasis is on the machine, rather than the product.
Finally, it is known to press manufacturers to include a tonnage gage in their presses to monitor the maximum cutting force. The manufacturers have used strain gages in various locations on the platen cutter to show the forces involved in cutting (see FIG. 1 which is a graphical illustration prepared by Bobst, Inc.) and includes a strain gage-based tonnage sensor on their latest platen die cutters. However, the shortcoming of this technique is that only the maximum forces are monitored and force values less than the maximum are ignored.
It is apparent from the above that there exists a need in the art for a system which monitors platen die cutting, and ensures a high quality of the end product, but which measures the forces dynamically. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.
Generally speaking, this invention fulfills these needs by providing a platen die cutting monitoring system, comprising a strain measurement means operatively connected to a platen die cutter, a signal conditioning means operatively connected to the strain measurement means, a waveform time averaging means operatively connected to the signal conditioning means, a waveform peak detection means operatively connected to the waveform time averaging means, and a peak comparison means operatively connected to the waveform peak detection means and the platen die cutter.
In certain preferred embodiments, the strain measurement means includes a strain gage. Also, the waveform peak detection means includes a digital filter. Finally, the peak comparison means includes a die cutter condition indication means.
In another further preferred embodiment, as the difference between the paper burst peak and the maximum force shrinks below a threshold limit, the platen begins to leave portions of the board uncut. If action to increase the difference in the peaks is taken before the difference falls below this threshold limit, then the paperboard is never left partially cut which ensures delivery of high-quality product from the platen cutter.
The preferred system, according to this invention, offers the following advantages: lightness in weight; good stability; good durability; excellent economy; excellent platen die cutter monitoring; and excellent cutting. In fact, in many of the preferred embodiments, these factors of economy, monitoring, and cutting are optimized to the extent that is considerably higher than heretofore achieved in prior, known systems.
The above and other features of the present invention, which will become more apparent as the description proceeds, are best understood by considering the following detailed description in conjunction with the accompanying drawings, wherein like characters represent like parts throughout the several views and in which: